Vehicle control apparatus

ABSTRACT

A vehicle control apparatus for implementing inter-vehicle distance control of a subject vehicle carrying the apparatus behind a preceding vehicle based on reflected waves from a target of the preceding vehicle. A target-pair distance is a distance between the target and a non-target reflection point that is closer to the subject vehicle than the target. A corrected distance calculator is configured to, in the presence of the target-pair distance being recognized, calculate a first corrected distance by subtracting the target-pair distance from a detected distance between the target and the subject vehicle, and in the absence of the target-pair distance being recognized, calculate a second corrected distance by subtracting an offset that is the previously set target-pair distance from the detected distance. A controller is configured to implement the inter-vehicle distance control based on the first or second corrected distance depending on the presence or absence of the target-pair distance being recognized.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims the benefit of priority fromearlier Japanese Patent Applications No. 2014-143707 filed Jul. 11,2014, the descriptions of which are incorporated herein by reference.

BACKGROUND

1. Technical Field

The present disclosure relates to a vehicle control apparatus forcontrolling travel of a vehicle carrying the apparatus to bring aninter-vehicle distance between the vehicle and a preceding vehicle to apreset target inter-vehicle distance.

2. Related Art

A known vehicle control apparatus, as disclosed in Japanese PatentApplication Laid-Open Publication No. 2013-164390, is configured tocontrol travel of a vehicle carrying the apparatus (hereinafter referredto as a subject vehicle) to bring an inter-vehicle distance between thesubject vehicle and a preceding vehicle to a preset target inter-vehicledistance. Such a vehicle control apparatus may use a radar device todetect a distance to the preceding vehicle and a relative speed of thepreceding vehicle. The radar device is configured to transmit radarwaves to the front of the subject vehicle and receive reflected waves toidentify, among peaks of a signal acquired from the reflected waves, apeak that is equal to or greater than a threshold value as a target,calculate a distance to the target and a relative speed and a lateralposition of the target to store target information about the target.

The vehicle control apparatus is configured to, based on the targetinformation, identify a target that is closest to the subject vehicleamong a plurality of targets as the preceding vehicle, and controltravel of the subject vehicle to bring the inter-vehicle distancebetween the subject vehicle and the target identified as the precedingvehicle to a preset target inter-vehicle distance.

However, for example, in a case where the rear end of the precedingvehicle has a small reflecting area, the reflected waves from the rearend of the preceding vehicle may be so weak that a target correspondingto the rear end of the preceding vehicle cannot be detected. In such acase, the inter-vehicle distance control cannot be properly implementedbehind the rear end of the preceding vehicle.

In consideration of the foregoing, exemplary embodiments of the presentdisclosure are directed to providing a vehicle control apparatus capableof properly implementing inter-vehicle distance control of a vehiclecarrying the apparatus behind a preceding vehicle.

SUMMARY

In accordance with an exemplary embodiment of the present invention,there is provided a vehicle control apparatus for implementinginter-vehicle distance control of a vehicle carrying the apparatusbehind a preceding vehicle based on reflected waves from a target thatis a reflecting portion of the preceding vehicle, the vehicle carryingthe apparatus being referred to as a subject vehicle, the reflectedwaves being radar waves transmitted to a front of the subject vehicleand then reflected from the target. The apparatus includes: a targetinformation acquirer configured to acquire target information about thetarget from the reflected waves, the target information including adetected distance from the subject vehicle to the target of thepreceding vehicle; a target-pair distance recognizer configured to, inthe presence of a target pair that is a pair of the target and anon-target reflection point that is closer to the subject vehicle thanthe target and belongs to the same preceding vehicle as the target,calculate and recognize a separation distance between the target and thenon-target reflection point of the target pair as a target-pairdistance; an offset setter configured to, when the target-pair distanceis recognized by the target-pair distance recognizer for a predeterminedperiod of time or more, set the target-pair distance as an offset; acorrected distance calculator configured to, when the target-pairdistance is recognized by the target-pair distance recognizer for thepredetermined period of time or more, calculate a first correcteddistance as an inter-vehicle distance between a rear end of thepreceding vehicle and the subject vehicle by subtracting the target-pairdistance from the detected distance, and when the target-pair distanceis recognized by the target-pair distance recognizer for less than thepredetermined period, calculate a second corrected distance as aninter-vehicle distance between the rear end of the preceding vehicle andthe subject vehicle by subtracting the offset set by the offset setterfrom the detected distance; and a controller configured to, when thetarget-pair distance is recognized by the target-pair distancerecognizer for the predetermined period of time or more, implement theinter-vehicle distance control based on the first corrected distancecalculated by the corrected distance calculator, and when thetarget-pair distance is recognized by the target-pair distancerecognizer for less than the predetermined period of time, implement theinter-vehicle distance control based on the second corrected distancecalculated by the corrected distance calculator.

In the presence of a pair of a target and a non-target reflection pointthat is a reflection point not recognized as a target and closer to thesubject vehicle than the target (the pair being referred to as a targetpair), a separation distance between the target and the non-targetreflection point of the target pair (the separation distance beingreferred to as a target-pair distance) is calculated. When thetarget-pair distance is recognized for a predetermined period of time ormore, the target-pair distance is set as an offset. Then, theinter-vehicle distance control is implemented based on the firstcorrected distance obtained by subtracting the target-pair distance fromthe detected distance to the target. When the target-pair distance isrecognized for less than the predetermined period of time, theinter-vehicle distance control is implemented based on the secondcorrected distance obtained by subtracting the offset from the detecteddistance to the target. This allows the inter-vehicle distance controlto be properly implemented whether or not the target-pair distance isrecognized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a vehicle control system in accordance withone embodiment of the present disclosure;

FIG. 2A is a functional block diagram of an ACC ECU;

FIG. 2B is a functional block diagram of a target-pair distancedeterminer;

FIGS. 3A and 3B are examples of detecting a rear end of a precedingvehicle;

FIGS. 4A to 4C are examples of a target-displacement determinationprocess performed in the ACC ECU;

FIG. 5 is an example of a target-pair distance determination processperformed in the ACC ECU;

FIG. 6 is a flowchart of an adaptive cruise control process performed inthe ACC ECU;

FIG. 7 is a flowchart of the target-displacement determination processperformed in the ACC ECU;

FIG. 8 is a flowchart of the target-pair distance determination processperformed in the ACC ECU;

FIG. 9 is an example of the target-pair distance determination processperformed in the ACC ECU;

FIG. 10 is a flowchart of an offset updating process;

FIG. 11 is a flowchart of an allowance/inhibition determination processperformed in the ACC ECU;

FIG. 12 is an example of the adaptive cruise control process performedin the ACC ECU; and

FIG. 13 is another example of the adaptive cruise control processperformed in the ACC ECU.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Embodiments of the present disclosure will now be described withreference to the accompanying drawings. A vehicle control apparatus inaccordance with one embodiment of the present disclosure is configuredto implement adaptive cruise control, that is, control a distance from avehicle carrying the apparatus (hereinafter referred to as a subjectvehicle) to a preceding vehicle detected by the radar or the like to atarget distance (referred to as a target inter-vehicle distance) as afunction of a speed of the preceding vehicle during following travel.When the preceding vehicle is stopped, the subject vehicle stops at aproper distance from the preceding vehicle. When travel of the precedingvehicle is restarted, the subject vehicle restarts the following travelwhile maintaining the distance to the preceding vehicle in accordancewith the speed of the preceding vehicle. When the preceding vehicleceases to be detected, the subject vehicle suspends the following traveland transitions to steady state cruising at a vehicle speed set by adriver of the subject vehicle.

The vehicle control apparatus of the present embodiment is equipped witha full speed range adaptive cruise control (ACC) function. The fullspeed range refers to a range from zero or a very low speed to apredefined high speed (e.g., a legal speed or an upper limit speed setby the driver or the like). Enabling the adaptive cruise control in thefull speed range (particularly in a low speed range) can reduce adriving load caused by frequent start/stop operations during a trafficjam. Although the inter-vehicle distance control, the following traveland the adaptive cruise control do not have the same meaning, they areused interchangeably in the present embodiment.

Referring to FIG. 1, an adaptive cruise control (ACC) apparatus 100includes a radar device 11, an adaptive cruise control (ACC) electroniccontrol unit (ECU) 12 (as the vehicle control apparatus), an engine ECU13, and a brake ECU 14. The ACC ECU 12 is configured to implement theadaptive cruise control in conjunction with the radar device 11 andother ECUs.

The radar device 11 and the ECUs 12-14 are connected communicatively toeach other via an onboard network, such as a controller area network(CAN). An adaptive cruise control (ACC) switch 15 is connected to theACC ECU 12 via an exclusive line, such as a serial communication line. Atransmission 16, a throttle motor 17, and a throttle sensor 18 areconnected to the engine ECU 13 via exclusive lines. A vehicle-speedsensor 19 and a brake actuator (brake ACT) 20 are connected to the brakeECU via exclusive lines.

Each of the radar device 11 and the ECUs 12-14 is an informationprocessor including a microcomputer, a power supply, a wiring harnessinterface and others. The microcomputer is of a well-known configurationincluding CPU, ROM, RAM, an input/output interface (I/O), and a CANcommunication device. The CPU loads programs stored in the ROM into theRAM and executes the programs to receive signals from the sensors viathe input/output interface and control the actuator and the like. TheCAN communication device transmits data to and receives data from theother ECUs 12-14 and others via the CAN. It will be appreciated thatpartitioning of functions described later between these ECUs 12-14 isexemplary and other partitioning of functions between these ECUs 12-14is also possible.

The radar device 11, which is an example of means for detecting adistance from the subject vehicle to the preceding vehicle, isconfigured to detect, for each target, a distance to the target and arelative speed and a lateral position of the target, and provide thedetection result to the ACC ECU 12.

The radar device 11 is configured to transmit a radio-frequency signalin a millimeter waveband as transmit waves. In the present embodiment,any one of a frequency-modulated continuous-wave (FMCW) approach and apulsed-radar approach and other well-known approaches may be used in theradar device 11 according to the type of transmission. The pulsed radaris configured to transmit the radar waves while changing thetransmission direction of the transmit waves in a predeterminedtransmission range and determine a direction of a target from thetransmission direction when reflected waves from the target arereceived. The FMCW approach will now be briefly explained.

The radar device 11 includes a transceiver 11 a for transmitting andreceiving radar waves. The transceiver 11 a is configured to transmitthe radar waves within a predetermined forward transmission range of theradar while linearly increasing the frequency with time at apredetermined increase rate and then linearly decreasing the frequencywith time at a predetermined decrease rate. The radar waves reflectedfrom a target forward of the subject vehicle are received by a pluralityof antennas. The received waves are mixed with the transmit waves togenerate a beat signal. The transceiver 11 a is attached to the frontside of the subject vehicle, such as a vehicle front grille, a bumper, aroof, a pillar or the like, at a position of a predetermined height.

A distance calculator 11 b is configured to calculate a distance to thetarget based on the beat signal. That is, there are relations:fr=(fb1+fb2)/2, andfd=(fb2-fb1)/2.

Here fb1 is a beat frequency in the upsweep interval, fb2 is a beatfrequency in the downsweep interval, fr is a Doppler frequency at arelative speed of zero, and fd is a Doppler frequency at a non-zerorelative speed (increased or decreased amount of frequency). Since theincrease rate and the decrease rate are known, there is a fixedrelationship between fr and the distance to the target. Therefore, thedistance calculator 11 b can calculate the distance to the target basedon fb1 and fb2.

A Doppler frequency that is a variation in frequency between thetransmit and receive waves is due to the Doppler effect. Therefore,there will be a fixed relationship between the relative speed and fd. Arelative speed calculator 11 c is configured to calculate the relativespeed based on fb1 and fb2. The relative speed is defined by the speedof the subject vehicle minus the speed of the preceding vehicle. Therelative speed takes a positive value when the distance decreases. Therelative speed takes a negative value when the distance increases.

To acquire the beat frequencies fb1, fb2 from the beat signal, forexample, Fourier transformation is applied to the beat signal in adigital signal processor (DSP) to analyze in which frequency band aprime component is present. Peaks occur at the power maxima in thespectrum of the beat signal. Thus, the beat frequencies are determinedby peak frequencies of the beat signal (i.e., frequencies at which peaksappear that are equal to or greater than a predetermined threshold).Such peaks are indicative of the presence of a target.

A relative speed calculator 11 c is configured to determine the beatfrequency fb1 from a peak in the upsweep interval and the beat frequencyfb2 from a peak in the downsweep interval. Thus, the distance to thetarget and the relative speed of the target can be detected. In thepresence of a plurality of targets in the transmission range of theradar, a plurality of peaks may be detected in each of the upsweep anddownsweep intervals.

A direction calculator 11 d is configured to calculate a direction (or alateral position) of a target relative to a frontal direction of thesubject vehicle. The transceiver 11 a has a plurality of receiveantennas. When the target is present, other than in front of the subjectvehicle, the beat signals received by the respective receive antennasare different in phase. Therefore, the direction of the target can becalculated using phase differences between the beat signals. Phases atthe beat frequencies can be calculated through the Fouriertransformation. In a monopulse method, the direction of the target canbe calculated as follows. When the target is not present in the frontaldirection of the subject vehicle, there is a path difference between thereflected waves received by two antennas. The path difference can bedetermined by a spacing between the two antennas and directions of thetwo antennas. Using the spacing between the receive antennas,wavelengths of the radio waves, and a fixed relationship between thephase difference and the path difference, the direction of the targetcorresponding to the path difference can be calculated from the phasedifference between the beat signals received by the two receiveantennas.

Alternatively, the direction of the target may be determined usingdigital beam forming (DBF) where a phased array antenna is realized bysignal processing. For example, advancing or retarding the phase of oneof beat signals received by two receive antennas that are different inphase allows the beat signals to match in phase where the signalintensity becomes maximal. Therefore, by changing the amount of phaseshift of the beat signals received by the respective receive antennasand calculating a sum of signal intensities, the target can be estimatedto be present in a direction corresponding to the amount of phase shiftat which the total signal intensity becomes maximal. In the presentembodiment, other methods for detecting the target direction includingmultiple signal classification (MUSIC) analysis, CAPON analysis andothers may be used.

The radar device 11 is configured to transmit target informationincluding the distance to the target and the relative speed and thedirection of the target to the ACC ECU 12 every scan. In each scan, asdescribed above, the frequency of the transmit wave is linearlyincreased in the upsweep interval and then linearly decreased in thedownsweep interval subsequent to the upsweep interval. In the presenceof a plurality of targets, the radar device 11 is configured to transmittarget information about each of the targets to the ACC ECU 12 everyscan. The radar device 11 is configured to update the target informationevery predetermined time period. The predetermined time period for oneupdate cycle is set to, for example, 50 msec.

The radar device 11 of the present embodiment is configured to, in thepresence of a target forward of the subject vehicle and a reflectionpoint that is not recognized as a target, but determined to belong tothe same preceding vehicle as the target, transmit information about thetarget forward of the subject vehicle and the reflection point to theACC ECU 12. Such a reflection point is hereinafter referred to as anon-target reflection point, and a pair of the target forward of thesubject vehicle and the non-target reflection point are referred to as atarget pair. For example, in the presence of a target forward of thesubject vehicle and a reflection point that is not recognized as atarget, but has a peak above a predetermined threshold and below thepeak of the target, the reflection point being closer to the subjectvehicle than the target forward of the subject vehicle and spaced apartfrom the target forward of the subject vehicle by a distance equal to orless than a predetermined value (e.g., 5 m), at a vertical position of aheight equal to or less than a vehicle height, at a lateral position ofa width equal to or less than a vehicle width relative to the target,the speed of the reflection point relative to the target being equal toor less than a predetermined value, the radar device 11 transmitsinformation about the target pair of the target forward of the subjectvehicle and the reflection point to the ACC ECU 12.

The ACC ECU 12 is configured to, based on the target information, acurrent vehicle speed, an acceleration and the like received from theradar device 11, transmit required drive forces or brake demand or thelike to another ECU.

The adaptive cruise control (ACC) switch 15 is configured to, whenoperated by the driver of the subject vehicle to permit the full speedrange adaptive cruise control, notify the ACC ECU 12 of it. For example,the adaptive cruise control (ACC) switch 15 is configured to notify tothe ACC ECU 12 operational signals, such as signals for turning ON orOFF of the full speed range adaptive cruise control, switching betweenan adaptive cruise control mode and a constant speed control mode,settings of a vehicle speed for constant speed travel, settings of theinter-vehicle distance, and others. In the present embodiment, it isassumed that the subject vehicle travels in the adaptive cruise controlmode. In the absence of a preceding vehicle, the subject vehicle remainsin the adaptive cruise control mode and travels at a constant speed,which will be described later in more detail.

The engine ECU 13 is configured to control the throttle motor 17 whilemonitoring a throttle opening detected by the throttle sensor 18. Forexample, based on a table showing throttle openings corresponding tovehicle speeds and acceleration instruction values, the engine ECU 13determines the throttle opening corresponding to the accelerationinstruction value received from the ACC ECU 12 and the current vehiclespeed. In addition, the engine ECU 13 determines the need for a gearchange based on an up-shift line and a down-shift line predefined forthe vehicle speed and the throttle opening, and if necessary, instructthe transmission 16 to change the gear. The transmission 16 may includea known mechanism, such as the automatic transmission (AT) or thecontinuously variable transmission (CVT).

The brake ECU 14 is configured to brake the subject vehicle bycontrolling opening and closing and a degree of opening of the valve ofthe brake ACT 20. The brake ACT 20 is configured to control theacceleration (deceleration) of the subject vehicle by increasing,maintaining, or decreasing the wheel cylinder pressure for each wheel.The brake ECU 14 is configured to brake the subject vehicle in responseto the acceleration instruction value from the ACC ECU 12.

The acceleration instruction value determined by the ACC ECU 12 istransmitted to the engine ECU 13 and the brake ECU 14. As a result, thethrottle motor 17 or the brake ACT 20 is controlled so that the subjectvehicle can travel following the preceding vehicle while maintaining thetarget inter-vehicle distance. Under control of the engine ECU 13 andthe brake ECU 14, the throttle opening may be increased, the throttleopening may be fully closed to decelerate the subject vehicle via enginebraking, air resistance, or rolling resistance, or the throttle openingmay be fully closed to decelerate the subject vehicle by the brake act20 increasing the wheel cylinder pressure.

(Functions of ACC ECU)

FIG. 2A shows a functional block diagram of the ACC ECU 12. The ACC ECU12 includes a target information acquirer 31, a target informationrecorder 32, a target information database (DB) 33, atarget-displacement determiner 34, a target-pair distance determiner 35,a distance selector 36, a followed-target determiner 37, anallowance/inhibition determiner 38, and a controller 39. In the presentembodiment, the adaptive cruise control is implemented by using targetinformation about the target that is closest to the subject vehicle(hereinafter referred to as a followed target) among a plurality oftargets that are different reflecting portions of the same precedingvehicle. The same preceding vehicle is an object having a plurality oftargets determined to have a substantially same speed while maintainingthe same spacing between each other.

The target information acquirer 31 is configured to acquire targetinformation about one or more targets from the radar device 11. Thetarget information recorder 32 stores the target information about eachtarget in the target information DB 33. More specifically, the targetinformation recorder 32 is configured to assign a unique identifier (ID)to each target and record a distance, a relative speed, and a lateralposition of each target. The target information acquirer 31 isconfigured to acquire information about the target pair from the radardevice 11.

For each target, the lateral position of the target is a position of thetarget in the widthwise direction of the subject vehicle relative to thelateral center of the subject vehicle, and is calculated from thedirection of the target and the distance to the target. The rightdirection from the lateral center of the subject vehicle may be definedas a positive direction, and the left direction from the lateral centerof the subject vehicle may be defined as a negative direction. In thefull speed range ACC, the subject vehicle follows the preceding vehiclethat is closest to the subject vehicle and does not have to followpreceding vehicles traveling in lanes other than the traveling lane ofthe subject vehicle that is a lane in which the subject vehicle istraveling. Therefore, the target or targets, information of which has tobe recorded, may belong to the preceding vehicle traveling in the samelane as the subject vehicle.

The radar device 11 is configured to transmit the target informationevery cycle time. The target information recorder 32 is configured toassign the same identifier to the same target and record the targetinformation in the target information DB 33. For example, when a lateralposition of a target received from the radar device 11 is displaced fromthe lateral position of the target recorded in the target information DB33 by a distance equal to or less than a maximum variation of thelateral position during one cycle, these targets are determined as thesame target. Alternatively, when a difference between a distance to atarget received from the radar device 11 and the distance to the targetrecorded in the target information DB 33 is equal to or less than amaximum variation of the distance during one cycle, these targets aredetermined as the same target. Thereafter, the target informationrecorder 32 updates the target information associated with the sameidentifier recorded in the target information DB 33.

The target-displacement determiner 34 is configured to, based on thetarget information stored in the target information DB 33, determinewhether or not a detected state of the identifier of the targetcorresponding to the rear end of the preceding vehicle has changed, thatis, determine whether or not the target with the shortest detecteddistance has been displaced. The rear end of the preceding vehicle isdetermined as the target that is closest to the subject vehicle which isspaced apart from the preceding vehicle by a distance equal to orgreater than a predetermined value. If the detected state of theidentifier of the target corresponding to the rear end of the precedingvehicle has changed, that is, if the target with the shortest distancehas been displaced, it is determined that the radar waves are overridingor underriding the rear end of the preceding vehicle. Thetarget-displacement determiner 34 is configured to estimate a distanceto the rear end of the preceding vehicle based on the relative speed Vz,and then output the estimated distance to the distance selector 36 as afirst inter-vehicle distance.

The target-pair distance determiner 35 is configured to, in the presenceof the target pair, calculate a separation distance between the targetand the non-target reflection point of the pair (hereinafter referred toas a target-pair distance). When the target-pair distance is recognizedfor a predetermined period of time or more, the target-pair distance ofthe target pair is set as an offset. The target-pair distance determiner35 is configured to, when the target-pair distance is being recognized,that is, when the target-pair distance is recognized for thepredetermined period of time or more, output a first corrected distance,as a second inter-vehicle distance, calculated by subtracting thetarget-pair distance from the detected distance to the target to thedistance selector 36, and when the target-pair distance is not beingrecognized, that is, when the target-pair distance is recognized forless than the predetermined period of time, output a second correcteddistance, as a second inter-vehicle distance, calculated by subtractingthe offset from the detected distance to the target to the distanceselector 36.

As shown in FIG. 2B, the target-pair distance determiner 35 includes atarget-pair distance recognizer 351, an offset setter 352, a correcteddistance calculator 353, a detected-distance determiner 354, an offseteraser 355, and a distance-change determiner 356. Processes performed inthe target-pair distance determiner 35 will be explained later in moredetail.

The distance selector 36 is configured to, for each target detected,select one of the detected distance acquired from the target informationacquirer 31, the first inter-vehicle distance acquired from thetarget-displacement determiner 34, and the second inter-vehicle distanceacquired from the target-pair distance determiner 35, as aninter-vehicle distance for the target. For example, the distanceselector 36 may select a shortest one of the detected distance, thefirst inter-vehicle distance, and the second inter-vehicle distance. Thefollowed-target determiner 37 is configured to determine one of thetargets detected that has a shortest inter-vehicle distance, as afollowed target.

The allowance/inhibition determiner 38 is configured to, based on theinter-vehicle distance and the identifier of the followed targetreceived from the followed-target determiner 37; determine whether ornot a detected state of the followed target is unstable. Theallowance/inhibition determiner 38 is configured to, when determiningthat the detected state of the followed target is unstable, inhibit thefollowing travel, and when the detected state of the followed targetbecomes stable, allow resumption of the following travel.

In some travel environments or weather, the reflected waves from thepreceding vehicle may become unstable despite the target-displacementdetermination process and the target-pair distance determinationprocesses being performed, which may cause the rear end of the precedingvehicle to become unable to be stably detected. In the presentembodiment, the allowance/inhibition determiner 38 is configured to,when the target determined as the followed target cannot be stablydetected under a certain condition, determine that the rear end of thepreceding vehicle is unable to be estimated and then instruct thecontroller 39 to make a switch to the direct operation by the driver.

The controller 39 is configured to implement the adaptive cruise controlbased on the inter-vehicle distance selected by the distance selector 36so that the subject vehicle can travel following the preceding vehiclewhile maintaining the target inter-vehicle distance.

The target-displacement determiner 34 and the target-pair distancedeterminer 35 will now be explained in more detail.

(Target-Displacement Determination)

In the case of the preceding vehicle being a vehicle with its rear endat a high position, such as a large vehicle, or a vehicle with its rearend at a low position, such as a low-floor vehicle, there may be adifference in height position between the rear end (or a rear surface)of the preceding vehicle and the radar device 11. Therefore, as theinter-vehicle distance between the preceding vehicle and the subjectvehicle decreases, the rear end of the preceding vehicle may becomeundetectable by the radar device 11 as a target.

For example, when as shown in FIG. 3A the preceding vehicle 70 and thesubject vehicle 80 are apart from each other and the rear end 72 of thepreceding vehicle 70 is within an area that spans a detection angle θ ofthe radar waves, the rear end 72 can be detected as a target. However,when as shown in FIG. 3B the preceding vehicle 70 approaches the subjectvehicle 80 so that the inter-vehicle distance is decreased and the rearend 72 is out of the area that spans the detection angle θ of the radarwaves, target displacement occurs, that is, the radar waves override therear end 72 of the preceding vehicle, or the radar waves underride therear end 72. In such a case, an anterior portion (e.g., a chassis or thelike) to the rear end 72 of the preceding vehicle may be detected, whichmay result in a distance between the preceding vehicle and the subjectvehicle less than a target inter-vehicle distance. In each of FIGS. 3Aand 3B, the distance L is a detected distance to a target recognized asthe rear end of the preceding vehicle 70 (hereinafter referred to as arear-end target). The rear-end target is a target that is closest to thesubject vehicle among the targets on the preceding vehicle. Such adetected distance is hereinafter referred to as a “rear-end detecteddistance”.

In the present embodiment, in the case that the radar waves areoverriding or underriding the rear end (i.e., the target displacementhas occurred), a variation of the inter-vehicle distance between thepreceding vehicle and the subject vehicle per predetermined time ofperiod is calculated using the relative speed between the precedingvehicle and the subject vehicle, and estimation of the inter-vehicledistance (i.e., calculation of the first inter-vehicle distance) isimplemented based on the variation of the inter-vehicle distance betweenthe preceding vehicle and the subject vehicle per predetermined time ofperiod. This can prevent the inter-vehicle distance between thepreceding vehicle and the subject vehicle from abruptly changing due tothe overriding or underriding of the radar waves.

In the radar device 11, the variation of the inter-vehicle distancebetween the preceding vehicle and the subject vehicle may be calculatedevery distance measurement period of time (e.g., 50 msec) using one ofthe following equations:ΔD1=D(i)−D(i−1)  (1)ΔD2=((Vz(i)+Vz(i−1))/2)×tm.  (2)

In the equation (1), a distance variation ΔD1 is calculated using aradar-measured distance as the detected distance. D(i) is a currentvalue of the detected distance, and D(i−1) is a previous value of thedetected distance. In the case that the radar waves are overriding orunderriding the rear end of the preceding vehicle, the current andprevious values of the detected distance may be detected distance valuesof targets with different identifies (see FIGS. 3A and 3B). In theequation (2), a distance variation ΔD2 is calculated using the relativespeed between the preceding vehicle and the subject vehicle. Vz(i) is acurrent value of the relative speed, and Vz(i−1) is a previous value ofthe relative speed. tm is a distance measurement period of time in theradar device 11. The distance variation ΔD1 calculated according to theequation (1) can reliably reflect the distance variation caused by thetarget displacement. The distance variation ΔD2 calculated according tothe equation (2) is less susceptible to the distance variation caused bythe target displacement. In the present embodiment, the estimateddistance is calculated as a the first inter-vehicle distance byiteratively adding the distance variation ΔD2 calculated according tothe equation (2) to the previous estimated distance.

When the radar waves override or underride the rear end of the precedingvehicle (the target displacement occurs), the distance variation ΔD1calculated using the current and previous values of the detecteddistance and the distance variation ΔD2 calculated using the current andprevious values of the relative speed develop differently. Therefore,monitoring developments of the distance variations ΔD1 and ΔD2, it canbe determined whether or not the target displacement has occurred, suchas overriding or underriding of the radar waves.

The increased inter-vehicle distance between the preceding vehicle andthe subject vehicle may increase after it is determined that the radarwaves are overriding or underriding the rear end of the precedingvehicle, that is, the target displacement has occurred. An increasedinter-vehicle distance between the preceding vehicle and the subjectvehicle may resolve the overriding or underriding of the radar waves.That is, the situation of FIG. 3B may transition to the situation ofFIG. 3A. In such a case, based on the detected distance between thepreceding vehicle 70 and the subject vehicle 80 (i.e., the rear-enddetected distance) and the estimated distance, it is determined whetheror not the overriding or underriding of the radar waves has beenresolved. More specifically, it can be determined that the overriding orunderriding of the radar waves has been resolved, when the detecteddistance A and the estimated distance B coincide with each other asshown in FIG. 4A, when a difference between the detected distance A andthe estimated distance B is within a predetermined range as shown inFIG. 4B, or when the detected distance A abruptly changes to approachthe estimated distance B as shown in FIG. 4C. After the overriding orunderriding of the radar waves is resolved, a switch to outputting therear-end detected distance as the first inter-vehicle distance is made,which allows a return to the adaptive cruise control based on therear-end detected distance to be made.

When the subject vehicle and the preceding vehicle are stopped whilst itis determined that the radar waves are overriding or underriding therear end of the preceding vehicle, a switch to calculating the firstinter-vehicle distance using the rear-end detected distance (themeasured distance from the radar device 11) and then outputting thecalculated first inter-vehicle distance is made. Then, an offset betweenthe rear-end detected distance and the estimated distance at the timethe vehicles are stopped is calculated. Whilst both the precedingvehicle and the subject vehicle are stationary, the inter-vehicledistance that is calculated by subtracting the offset from the rear-enddetected distance is outputted as the first inter-vehicle distance. Thisallows the inter-vehicle distance between the rear end of the precedingvehicle and the subject vehicle to be recognized while they arestationary and to reflect the distance variations that occur while thevehicles are stationary.

(Target-Pair Distance Determination Process)

In the present embodiment, the target that is forward of the subjectvehicle and closest to the subject vehicle is recognized as a target tobe followed in the adaptive cruise control. If the target is not atarget corresponding to the rear end of the preceding vehicle (but atarget corresponding to a middle portion of the preceding vehicle),there may be another reflection point that is closer to the subjectvehicle than the target.

For example, in the case of the preceding vehicle 70 having a carcarrier as shown in FIG. 5, a small area of the rear end of thepreceding vehicle may lead to weak reflected waves from the rear end.Therefore, another reflection point 72 that is not recognized as atarget may appear at a position closer to the subject vehicle than thetarget 73. Preferably, in such a case, the adaptive cruise control isimplemented taking into account the reflection point 72. Such anotherreflection point 72 is hereinafter referred to as a non-targetreflection point.

In the present embodiment, such a reflection point 72 that is notrecognized as a target and the target 73 form a target pair as definedabove. The ACC ECU 12 is configured to, upon detecting such a targetpair, calculate a target-pair distance L2 between the target 73 and thenon-target reflection point 72. Further, when the target-pair distanceL2 is recognized for a predetermined period of time or more, thetarget-pair distance L2 is retained as an offset L3. When thetarget-pair distance is being recognized, that is, when the target-pairdistance L2 is recognized for the predetermined period of time or more,a second inter-vehicle distance that is calculated by subtracting thetarget-pair distance L2 from the detected distance L1 is outputted tothe distance selector 36. When the target-pair distance is not beingrecognized, that is, when the target-pair distance L2 is recognized forless than the predetermined period of time, a corrected distance that iscalculated by subtracting the offset L3 from the detected distance L1 tothe target 73 is outputted to the distance selector 36 as a secondinter-vehicle distance.

Principally, in the present embodiment, the distance to and thedirection of the rear end of the preceding vehicle traveling forward ofthe subject vehicle are measured by the radar device 11. Based on themeasurement result, the adaptive cruise control is implemented. However,without stable detection of the rear end of the preceding vehicle, afailure might occur in controlling the inter-vehicle distance to thetarget inter-vehicle distance.

For example, when there is a difference in height position between therear end of the preceding vehicle (e.g., a rear side portion) and theradar device 11, the rear end of the preceding vehicle may be no longerwithin the detection zone (that spans a detection angle θ of the radarwaves) of the radar device 11 depending on an actual distance betweenthe preceding vehicle and the subject vehicle. In such a case, despitethe presence of the rear end of the preceding vehicle, the radar device11 may fail to detect the rear end of the preceding vehicle, as shown inFIGS. 3A and 3B. To overcome such a disadvantage due to the targetdisplacement, the target-displacement determiner 34 is configured todetermine whether or not the target displacement has occurred, and whendetermining that the target displacement has occurred, calculate thefirst inter-vehicle distance calculated by subtracting the offset fromthe detected distance.

In the case of a small area of the rear end portion of the precedingvehicle, the reflected waves from the rear end may be weak in intensity.Due to the weakness of the reflected waves, another reflection pointthat is not recognized as a target may appear at a position closer tothe subject vehicle than the target closest to the subject vehicle. Insuch a case, a failure might occur in controlling the inter-vehicledistance to the target distance, as shown in FIGS. 5A and 5B. Toovercome such a disadvantage due to the presence of the target paircaused by the weakness of the reflected waves, the target-pair distancedeterminer 35 is configured to calculate the second inter-vehicledistance calculated by subtracting the target-pair distance or theoffset from the detected distance.

(Active Cruise Control Process)

An active cruise control process to be performed in the ACC ECU 12 willnow be explained with reference to a flowchart of FIG. 6. This processis repeatedly performed every predetermined period of time.

Referring to FIG. 6, in step S10, the target information acquirer 31acquires the target information from the radar device 11. In step S11,the target information recorder 32 assigns the same identifier to thesame target, and record the target information in the target informationDB 33.

In step S12, a target-displacement determination process is performed,where the target-displacement determiner 34 determines, from thedetected state of the rear end of the preceding vehicle, whether or notthe radar waves are overriding or underriding the rear end of thepreceding vehicle, and when determining that the radar waves areoverriding or underriding the rear end of the preceding vehicle,calculate the first inter-vehicle distance.

In step S13, a target-pair determination process is performed, where thetarget-pair distance determiner 35 is configured to, in the presence ofthe target pair, calculate the target-pair distance. When thetarget-pair distance is recognized for the predetermined period of timeor more, the target-pair distance of the target pair is calculated as anoffset. Depending on whether or not the target-pair distance is beingrecognized, the target-pair distance determiner 35 calculates the secondinter-vehicle distance that is the detected distance corrected by thetarget-pair distance or the offset.

In step S14, a distance selection process is performed, where for eachtarget detected, the distance selector 36 selects a shortest one of thedetected distance, the first inter-vehicle distance, and the secondinter-vehicle distance, and associates the target with the selectedinter-vehicle distance. In step S15, a followed-target determinationprocess is performed, where the followed-target determiner 37 determinesthe target associated with a shortest one of the inter-vehicle distancesselected in step S14 for the respective targets as a followed target.

In step S16, an allowance/inhibition determination process is performed,where the allowance/inhibition determiner 38 determines whether or notthe followed target is stably detected, and when it is determined thatthe followed target is stably detected, allows the controller 39 toimplement the adaptive cruise control to follow the followed targetdetermined in step S15. When it is determined that the followed targetis not stably detected, the allowance/inhibition determiner 38 inhibitsthe controller 39 from implementing the adaptive cruise control andinstructs the controller 39 to make a switch to the direct operation bythe driver.

The calculation of the first inter-vehicle distance implemented in stepS12 by the target-displacement determiner 34 may be performed in theexemplary situation shown in FIGS. 3A and 3B, and the calculation of thesecond inter-vehicle distance implemented in step S13 by the target-pairdistance determiner 35 may be performed in the exemplary situation shownin FIGS. 5A and 5B. The calculation of the first inter-vehicle distanceand the calculation of the second inter-vehicle distance may beselectively implemented depending on in what state the subject vehicletravels following the preceding vehicle.

(Target-Displacement Determination Process)

The target-displacement determination process in step S12 of FIG. 6 willnow be explained. In FIG. 7, it is determined in step S20 whether or nota criterion for determining the target displacement is met. Thecriterion is met if all first to third conditions are met. The firstcondition is that the detected distance is equal to or less than apredetermined value (e.g., equal to or less than 30-40 m), the secondcondition is that the relative speed is within a predetermined range,and the third condition is that the vehicle speed is less than apredetermined value (e.g., less than 200-100 km/h).

If it is determined in step S20 that the criterion is met, then in step21 it is determined whether or not the radar waves are overriding orunderriding the rear end of the preceding vehicle, that is, the targetdisplacement has occurred. In step S21, the determination is made basedon the difference in development between the variation of the detecteddistance and the variation of the relative speed. More specifically, thedistance variation ΔD1 calculated from the previous and current valuesof the detected distance and the distance variation ΔD2 calculated fromthe previous and current values of the relative speed are compared witheach other. If the value of ΔD1-ΔD2 is equal to or greater than apredetermined value, then it is determined that the radar waves areoverriding or underriding the rear end of the preceding vehicle, thatis, the target displacement has occurred.

Alternatively, it may be determined whether or not the distancevariation ΔD1 calculated from the previous and current values of thedetected distance is equal to or greater than a predetermined value. Ifit is determined that the distance variation ΔD1 is equal to or greaterthan the predetermined value, then it may be determined that the radarwaves are overriding or underriding the rear end of the precedingvehicle, that is, the target displacement has occurred.

If it is determined in step S21 that the target displacement hasoccurred, then in step S22 it is determined whether or not both thepreceding vehicle and the subject vehicle are traveling. If it isdetermined in step S22 that both the preceding vehicle and the subjectvehicle are traveling, then in step S23 the estimated distance iscalculated as the first inter-vehicle distance. If both the precedingvehicle and the subject vehicle are stationary, then in step 24 it isdetermined whether or not the offset between the estimated distanceobtained at the time both the preceding and subject vehicles are stoppedand the rear-end detected distance is uncalculated. If the offset isuncalculated, then in step S25 the offset is calculated by subtractingthe estimated distance obtained at the time both the preceding andsubject vehicles are stopped from the rear-end detected distance.

If the offset has been calculated, then in step S26 the firstinter-vehicle distance is calculated by subtracting the offset from therear-end detected distance.

If it is determined in step S20 that the criterion is not met or if thetarget displacement has not occurred, then in step S27 the calculationof the estimated distance is suspended.

(Target-Pair Distance Determination Process)

The target-pair distance determination process in step S13 of FIG. 6will now be explained. Referring to FIG. 8, in step S301, it isdetermined whether or not the detected distance between the precedingvehicle (target) and the subject vehicle is less than a predeterminedvalue. If in step S301 it is determined that the detected distance isless than the predetermined value, then in step S302 the target-pairdistance is calculated in the presence of the target pair. In step S303,it is determined whether or not the target-pair distance is recognizedfor a predetermined period of time or more. For example, as shown inFIG. 9, if the target-pair distance is detected a predetermined numberof times or more within a set time, then it is determined that thetarget-pair distance is being recognized and a flag is set.

If it is determined in step S303 that the target-pair distance isrecognized for the predetermined period of time or more, then in stepS304 the target-pair distance is set as an offset. Subsequently, in stepS305, a corrected distance, as a second inter-vehicle distance, iscalculated by subtracting the target-pair distance from the detecteddistance.

If it is not determined in step S303 that the target-pair distance isrecognized for the predetermined period of time or more, then in stepS306 it is determined whether or not the offset has been set. If it isdetermined that the offset has been set, then in step S307 a correcteddistance, as a second inter-vehicle distance, is calculated bysubtracting the offset from the detected distance. If it is determinedthat the offset is unset, then in step S308 the second inter-vehicledistance is set to the detected distance.

If in step S301 it is determined that the detected distance between thepreceding vehicle (target) and the subject vehicle is equal to orgreater than the predetermined value, then in step S309 it is determinedwhether or not the offset has been set. If in step S309 it is determinedthat the offset has been set, then in step S310 the offset is erased (orinvalidated). For example, the offset is set to zero. If in step S309 itis determined that the offset is unset, then the process ends.

Referring again to FIG. 2B, the target-pair distance recognizer 351 isresponsible for execution of the operation in steps S302, the offsetsetter 352 is responsible for execution of the operations in steps S303and S304, the corrected distance calculator 353 is responsible forexecution of the operations in steps S305 and S307, thedetected-distance determiner 354 is responsible for execution of theoperation in step S301, and the offset eraser 355 is responsible forexecution of the operation in step S310.

A low reflection signal level from the non-target reflation point maycause the detected position of the non-target reflation point to bevaried forward or backward in the traveling direction. If the non-targetreflection point is displaced forward in the traveling direction, thetarget-pair distance will decrease. If the offset calculated based onthe target-pair distance is updated to be decreased, the inter-vehicledistance between the preceding vehicle and the subject vehicle maybecome less than the target inter-vehicle distance. Therefore,preferably, the target-pair distance is only updated to be increased.

Referring to FIG. 10, in step S41, it is determined whether or not thetarget-pair distance is being recognized. If in step S41 it isdetermined that the target-pair distance is being recognized, then instep S42 a counter N is incremented by one, where the initial value ofthe counter N is set to zero. In step S43, it is determined whether ornot the counter N is equal to or greater than a predetermined thresholdvalue. The predetermined threshold value is a positive integer greaterthan one and may be set by experiments. If in step S43 it is determinedthat the counter N is equal to or greater than the predeterminedthreshold value, then in step S44 it is determined whether or not thecurrent value of the target-pair distance is greater than the previousvalue of the target-pair distance. If in step S44 the current value ofthe target-pair distance is greater than the previous value, then instep S45 the offset is updated to be increased. In step S46, the counterN is reset. If in step S41 it is determined that the target-pairdistance is not being recognized, then in step S46 the counter N isreset. In addition, if in step S43 it is determined that the counter Nis less than the predetermined threshold value or if in step S44 thecurrent value of the target-pair distance is equal to or less than theprevious value, then the process ends. The offset setter (352, S303,S304) is configured to, when an increased target-pair distance ismaintained for a predetermined period of time or more, update the offsetto be increased.

(Allowance/Inhibition Determination Process)

The allowance/inhibition determination process in step S16 of FIG. 6will now be explained. The following processing steps are repeatedlyperformed under situations where the subject vehicle is not switchinglanes. Referring to FIG. 11, in step S51, it is determined whether ornot the adaptive cruise control is active. If in step S51 it isdetermined that the adaptive cruise control is active, then in step S52it is determined whether or not the subject vehicle is approaching thepreceding vehicle, that is, whether or not the subject vehicle has comewithin a certain proximity of the preceding vehicle. If in step S52 itis determined that the subject vehicle has come within a certainproximity of the preceding vehicle, then in step S53 it is determinedwhether or not the target information for identifying the rear end ofthe preceding vehicle is unacquirable. For example, in the case that thespecific target on the preceding vehicle is unexpectedly much displacedforward or in the case that the target information is no longer stablyacquired, it is determined that the target information is unacquirable.If in step S53 it is determined that the target information isunacquirable, then in step S54 the adaptive cruise control is suspendedor inhibited and the subject vehicle transitions to the direct operationby the driver. A user may then be notified that the adaptive cruisecontrol is suspended and the subject vehicle has transitioned to thedirect operation by the driver, via visual messages on a display screenof a display (not shown), audio messages from a speaker (not shown) orthe like. While the adaptive cruise control is suspended, acquisition ofinformation from the radar device 11, the engine ECU 13, and the brakeECU 14 is continued.

If in step S52 it is determined that the subject vehicle is not within acertain proximity of the preceding vehicle, then in step S55 it isdetermined whether or not the speed of the subject vehicle is within apredetermined low speed range. That is, it is determined whether or notthe speed of the subject vehicle is less than a predetermined value. Ifin step S55 it is determined that the speed of the subject vehicle iswithin the predetermined low speed range, then the process proceeds tostep S53. If in step S53 it is determined that the target information isunacquirable, then the process proceeds to step S54. If in step S55 itis determined that the speed of the subject vehicle is out of thepredetermined low speed range, then the process ends. Then the adaptivecruise control is continued to be active.

If in step S51 it is determined that the adaptive cruise control isinactive, that is, the adaptive cruise control was suspended in step S54in the previous cycle, then the process proceeds to step S56. In stepS56, it is determined whether or not the target information foridentifying the rear end of the preceding vehicle is acquirable. Forexample, in the case that the inter-vehicle distance between thepreceding vehicle and the subject vehicle is equal to or greater than apredetermined value or in the case that the relative speed of thepreceding vehicle is equal to or greater than a predetermined value,leading to an increased inter-vehicle distance between the precedingvehicle and the subject vehicle, it is determined that the targetinformation is acquirable.

If in step S56 it is determined that the target information isacquirable, then the process proceeds to step S57, where the inhibitionof the adaptive cruise control is removed. That is, the adaptive cruisecontrol is allowed to be reactivated. If in step S56 it is determinedthat the target information is unacquirable, then the process ends. Insuch a case, the reactivation of the adaptive cruise control iscontinued to be inhibited.

EXAMPLES

Examples of the present embodiment will now be explained. FIG. 12 showsan example where it is assumed that the first inter-vehicle distance isa shortest inter-vehicle distance between the preceding vehicle and thesubject vehicle. In FIG. 12, “A” represents the detected distanceacquired from the radar device 11 and “B” represents the estimateddistance B substantially equal to the actual inter-vehicle distancebetween the preceding vehicle and the subject vehicle. In this example,it is assumed that the preceding vehicle is a large low-floor vehicle.

If before time t1 the preceding vehicle 70 and the subject vehicle 80are apart from each other, the detection zone that spans the detectionangle 8 of the radar waves may include the rear end 72 of the precedingvehicle 70, which allows the rear end 72 of the preceding vehicle 70 tobe detected as a target (see FIG. 3A). In such a situation, it isdetermined that the radar waves are neither overriding nor underridingthe rear end 72 of the preceding vehicle 70. Therefore, theinter-vehicle distance between the preceding vehicle and the subjectvehicle may be controlled based on the detected distance from the radardevice 11.

If at time t1 the inter-vehicle distance between the preceding vehicleand the subject vehicle decreases as the subject vehicle 80 approachesthe preceding vehicle 70, the rear end 72 of the preceding vehicle 70 isplaced out of the detection zone that spans the detection angle θ of theradar waves, so that the rear end 72 of the preceding vehicle 70 becomesundetectable (see FIG. 3B). In such a situation, it is determined thatthe radar waves are overriding or underriding the rear end 72 of thepreceding vehicle 70. Then, the adaptive cruise control is implementedusing the estimated distance calculated based on the relative speed Vz.

If at time t2 the subject vehicle and the preceding vehicle stop forwaiting at traffic lights or the like, a difference between theestimated vehicle and the detected distance during the stationary stateis stored as the offset ΔD. The ACC ECU 12 calculates the firstinter-vehicle distance by subtracting the offset ΔD from the detecteddistance as the inter-vehicle distance during the stationary state.

If at time t3 the preceding vehicle and the subject vehicle are started,switching to the adaptive cruise control based on the estimated distanceis made due to underriding of the radar waves. If at time t4 theinter-vehicle distance between the preceding vehicle and the subjectvehicle exceeds the predetermined value, the radar device 11 becomesable to detect the rear end 72 of the preceding vehicle 70, which allowsthe determination of whether or not the radar waves are underriding therear end 72 of the preceding vehicle 70 to be ceased. Instead of theestimated distance, the detected distance is recognized as theinter-vehicle distance. Then, the adaptive cruise control based on theactual inter-vehicle distance acquired from the radar device 11 isimplemented.

Another example of the present embodiment will now be explained withreference to FIG. 13. FIG. 13 shows an example where it is assumed thatthe second inter-vehicle distance calculated in the target-pair distancedetermination process is determined to be a shortest inter-vehicledistance between the preceding vehicle and subject vehicle.

The target-pair distance determination process is initiated before timet11. Upon detection of the target pair, the target-pair distance iscalculated. If at time t11 it is determined that the target-pairdistance has been detected for the predetermined period of time or more,counting of the counter N is started and then the target-pair distanceis recorded as the offset. At or after time t11, the adaptive cruisecontrol based on the second inter-vehicle distance calculated bysubtracting the target-pair distance from the detected distance isimplemented.

If at time t12 it is determined that the target-pair distance is nolonger recognized, then the counter N is reset (N=0). It is notdetermined until time t13 that the target-pair distance is beingrecognized. Therefore, the adaptive cruise control based on the secondinter-vehicle distance calculated by subtracting the offset from thedetected distance is implemented.

If at time t13 it is determined that the target-pair distance is beingrecognized, the counting of the counter N is restarted. If at time t14it is determined that the counter N is equal to or greater than thethreshold value TH and the target-pair distance is increased, the offsetis updated to be increased by an increase a in the target-pair distance.Thereafter, the counter N is reset (N=0).

The present embodiment of this disclosure can provide the followingadvantages.

(i) In the presence of a pair of a target and a non-target reflectionpoint that is a reflection point not recognized as a target and closerto the subject vehicle than the target (the pair being referred to as atarget pair), a separation distance between the target and thenon-target reflection point of the target pair (the separation distancebeing referred to as a target-pair distance) is calculated. When thetarget-pair distance is recognized for a predetermined period of time ormore, the target-pair distance is set as an offset. Then, the adaptivecruise control is implemented based on the first corrected distanceobtained by subtracting the target-pair distance from the detecteddistance to the target. When the target-pair distance is recognized forless than the predetermined period of time, the adaptive cruise controlis implemented based on the second corrected distance obtained bysubtracting the offset from the detected distance to the target. Thisallows the adaptive cruise control to be properly implemented whether ornot the target-pair distance is recognized.

(ii) When in the presence of the offset stored the inter-vehicledistance between the preceding vehicle and the subject vehicle increasesso that the target-pair distance becomes detectable, the offset iserased. In situations where the target-pair distance is detectable, thisallows the adaptive cruise control to be implemented based on thedetected distance corrected by the actual target-pair distance.

(iii) When the increased target-pair distance is maintained for thepredetermined period of time or more (see FIG. 10), the offset isupdated to be increased. This can properly ensure the adaptive cruisecontrol in situations where the increased target-pair distance ismaintained.

(Modifications)

Some modifications to the above embodiment that may be devised withoutdeparting from the spirit and scope of the present invention.

(a) In the target-displacement determination process, when the detecteddistance abruptly decreases in a situation where in step S21 it isdetermined that the radar waves are underriding the rear end of thepreceding vehicle, it is likely that the radar device 11 has detectedthe rear end of the preceding vehicle. Therefore, instead of theestimated distance, the detected distance may be used as theinter-vehicle distance. Besides, when the subject vehicle is spacedapart from the preceding vehicle by a distance such that the rear end ofpreceding vehicle is detectable by the radar device 11 of the subjectvehicle, instead of the estimated distance, the detected distance may beused as the inter-vehicle distance. Whether or not the rear end of thepreceding vehicle is detectable by the radar device 11 of the subjectvehicle can be determined depending on the specification of the radardevice 11.

(b) In the target-pair distance determination process, when a targetrecognized by the radar device 11 is displaced toward the subjectvehicle through, for example, an unexpected anterior-to-posterior targetchange, the detected distance may be excessively decreased by the offsetcorrection. Therefore, when the detected distance to the targetrecognized by the radar device 11 abruptly decreases, the offsetcorrection may be suspended. More specifically, the target-pair distancedeterminer 35 may further include a distance-change determiner 356configured to determine whether or not the detected distance is abruptlydecreased, and the corrected distance calculator 353 may be configuredto, when it is determined by the distance-change determiner 356 that thedetected distance is abruptly decreased, suspend the calculation of thesecond corrected distance. This can suppress such a disadvantage thatthe detected distance to the recognized target may be excessivelydecreased by the offset correction.

(c) In the target-pair distance determination process as above, whenanother target pair is newly recognized after it is determined that thedetected distance is abruptly decreased and then the offset correctionis suspended, the target-pair distance for the newly recognized targetmay be set as an offset. In such a case, the offset correction may beunsuspended or resumed immediately. More specifically, the correcteddistance calculator 353 is configured to, when another target pair isnewly recognized by the target-pair distance recognizer 351 after it isdetermined by the distance-change determiner 356 that the detecteddistance is abruptly decreased and then the calculation of the secondcorrected distance is suspended, set the target-pair distance for thenewly recognized target pair as an offset and resume the calculation ofthe second corrected distance.

(d) In the target-pair distance determination process, the ACC ECU 12may be configured to directly acquire the reflected wave signal of theradar device 11, where the reflected waves may be analyzed in the ACCECU 12, thereby enabling the ACC ECU 12 to determine the presence orabsence of a non-target reflection point that is a reflection pointother than the target recognized by the radar device 11 and closer tothe subject vehicle than the target.

(e) In the embodiment described in detail above, the radar device 11 isused as a distance detection sensor. Alternatively or additionally, acamera or a stereoscopic camera may be used. Also with use of the cameraor the stereoscopic camera, similar information about the target may beacquired. The radar and the stereoscopic camera are different in thedetection range and accuracy. Therefore, advantageously, the subjectvehicle may be equipped with both the radar and the stereoscopic camera,where the radar and the stereoscopic camera can be complementarily usedto implement sensor fusion based distance detection. That is, in thesensor fusion based distance detection, the stereoscopic camera may beused to acquire short-range distance information and a lateral positionof a near target that is difficult for the radar device 11 to detect,and the radar device 11 may be used to acquire mid- to long rangedistance information and a lateral position of a remote target that isdifficult for the stereoscopic camera to detect. Besides, the targetinformation about the preceding vehicle or the like may be acquiredusing a ranging sensor that uses sound waves, light waves, radio wavesor the like.

(f) The vehicle control apparatus may be equipped with not only the ACCfunction, but also either or both of pre-crash safety (PCS) andlane-keeping assist (LKA) functions. In such a case, theallowance/inhibition determiner 38 may be configured such that, in stepS54 where the adaptive cruise control is suspended and the switch to thedirect operation by the driver is made, only the adaptive cruise controlmay be suspended, or not only the adaptive cruise control, but also thePCS or LKA function may be suspended.

Whereas particular embodiments of the present invention have beendescribed above as examples, it will be appreciated that variations ofthe details may be made without departing from the scope of theinvention. One skilled in the art will appreciate that the presentinvention can be practiced by other than the disclosed embodiments, allof which are presented in this description for purposes of illustrationand not of limitation. It is noted that equivalents of the particularembodiments discussed in this description may result in the practice ofthis invention as well. Therefore, reference should be made to theappended claims rather than the foregoing discussion or examples whenassessing the scope of the invention in which exclusive rights areclaimed.

What is claimed is:
 1. A vehicle control apparatus for implementinginter-vehicle distance control of a vehicle carrying the apparatusbehind a preceding vehicle based on reflected waves from a target thatis a reflecting portion of the preceding vehicle, the vehicle carryingthe apparatus being referred to as a subject vehicle, the reflectedwaves being radar waves transmitted to a front of the subject vehicleand then reflected from the target, the apparatus comprising: a targetinformation acquirer configured to acquire target information about thetarget from the reflected waves, the target information including adetected distance from the subject vehicle to the target of thepreceding vehicle; a target-pair distance recognizer configured to, inthe presence of a target pair that is a pair of the target and anon-target reflection point that is closer to the subject vehicle thanthe target and belongs to the same preceding vehicle as the target,calculate and recognize a separation distance between the target and thenon-target reflection point of the target pair as a target-pairdistance; an offset setter configured to, when the target-pair distanceis recognized by the target-pair distance recognizer for a predeterminedperiod of time or more, set the target-pair distance as an offset; acorrected distance calculator configured to, when the target-pairdistance is recognized by the target-pair distance recognizer for thepredetermined period of time or more, calculate a first correcteddistance as an inter-vehicle distance between a rear end of thepreceding vehicle and the subject vehicle by subtracting the target-pairdistance from the detected distance, and when the target-pair distanceis recognized by the target-pair distance recognizer for less than thepredetermined period of time, calculate a second corrected distance asan inter-vehicle distance between the rear end of the preceding vehicleand the subject vehicle by subtracting the offset set by the offsetsetter from the detected distance; and a controller configured to, whenthe target-pair distance is recognized by the target-pair distancerecognizer for the predetermined period of time or more, implement theinter-vehicle distance control based on the first corrected distancecalculated by the corrected distance calculator, and when thetarget-pair distance is recognized by the target-pair distancerecognizer for less than the predetermined period of time, implement theinter-vehicle distance control based on the second corrected distancecalculated by the corrected distance calculator.
 2. The apparatus ofclaim 1, further comprising: a detected-distance determiner configuredto determine whether or not the detected distance is equal to or greaterthan a predetermined value, and an offset eraser configured to, when itis determined by the detected-distance determiner that the detecteddistance is equal to or greater than the predetermined value, erase theoffset that was set previously.
 3. The apparatus of claim 1, wherein theoffset setter is configured to, when an increased target-pair distanceis maintained for a predetermined period of time or more, update theoffset to be increased.
 4. The apparatus of claim 1, further comprisinga distance-change determiner configured to determine whether or not thedetected distance is abruptly decreased, wherein the corrected distancecalculator is configured to, when it is determined by thedistance-change determiner that the detected distance is abruptlydecreased, suspend the calculation of the second corrected distance. 5.The apparatus of claim 4, wherein the corrected distance calculator isconfigured to, when another target pair is newly recognized by thetarget-pair distance recognizer after it is determined by thedistance-change determiner that the detected distance is abruptlydecreased and then the calculation of the second corrected distance issuspended, resume the calculation of the second corrected distance usingthe target-pair distance for the newly recognized target pair set as anoffset.